1. Field of the Invention
The present invention relates to a length measure apparatus and the method for measuring, and more particularly to a length measure apparatus and the method for measuring that can overcome errors from the operator's vision and the measure apparatus.
2. Description of Related Art
A conventional profile projector in accordance with the prior art shown in FIG. 5 comprises a base member (81) and a worktable (82) mounted on the top of the base member (81). A project box (83) is mounted to the top of the worktable (82). A screen (84) is rotatably attached to the project box (83) and made of frosted glass. Multiple clamps (841) are mounted on the project box (83) around the screen (84) for securing a transparent film on the screen (84). A adjust knob (85) is rotatably mounted to the project box (83) for rotating the screen (84). A first adjust roller (86) is pivotally mounted to the worktable (82) for reciprocally moving the worktable (82) along an X-axis of the worktable (82) and a second adjust roller (87) is pivotally mounted to the worktable (82) for reciprocally moving the worktable (82) along a Y-axis of the worktable (82).
A light source (not shown) is mounted in the worktable (82) for projecting the outline of the workpiece on the worktable (82) to the project box (83) and show on the screen (84). The transparent film has a standard line (88) printed thereon and used to contrast with the outline of the workpiece for measuring.
For example, to measure the length relative to the X-axis, a transparent film with a standard line (88) is clamped the screen (84) by using the multiple clamps (841) and the workpiece is put on the worktable of the profile projector. The operator rotates the first adjust roller (86) to make a first side of the workpiece flush with the standard line (88) and make the linear scale (not shown) in the worktable show zero. Next, the operator rotates the first adjust roller (86) again to make a second side of the workpiece flush with the standard line (88) and real the data from the linear scale relative to the X-axis of the workpiece.
However, the standard line (88) usually has a width about 0.3 mm for an easy operation. However, with reference to FIG. 6, the width will cause a certain error when aiming the profile (9) of the workpiece at the standard line (88), that is, the operator will be of the opinion that the profile of the workpiece is aimed at the standard line (88) when the profile of the workpiece moved within the width of the standard line (88). Consequently, different operator has a different result of measuring.
For example, to measure the angle of profile of the workpiece, a transparent film with a standard line (88) is secured on the screen (84) by the multiple clamps (841). The operator adjusts the adjust knob (85) to rotate around the screen (84) and the rotating range of the screen (84) is measured by a rotary encoder (not shown) due to a series of scales on a periphery of the screen (84). The scales of the screen (84) are set zero when the standard line (88) flush with a datum of the profile of the workpiece after that the screen (84) is rotated again to make the standard line flush with another side of the profile of the workpiece and the operator can read the angle value of the profile of the workpiece by the series of scales on the periphery of the screen (84).
However, the width of the standard line will cause an error the same as the embodiment described above. Furthermore, the round screen (84) is made of frosted glass and has a certain error of the roundness of the screen (84). The error of the roundness of the screen (84) may influence the precision of the scales on the periphery of the screen (84). The errors of the roundness of the screen (84) and the scales on the periphery of the screen (84) are added up to influence the measure precision of the length measure apparatus.
The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional length measure apparatus and the method for measuring.